Computer Graphics World

JULY 2010

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n n n n Simulation maximum forces at different velocities,” Ste- phens explains. “She does this for legs, hips, and back, isolating joints. Sixty subjects per joint. She gets high velocity and low velocity to collect the maximum.” Soon, Stephens will feed the re- sulting dynamic strength curves to Santos. Currently, the manufacturing and engi- neering department uses Jack and Jill, digital humans from Siemens PLM Software and de- veloped at the University of Pennsylvania, to crawl under cars, under car hoods, and sit in passenger seats. “Jack still has a home with us, and so does Jill, but the area they can’t analyze is dynamic work,” says Stephens. “A lot of people are fa- miliar with ergonomics in terms of setting up driver interfaces and layout of controls in a car. Te focus for assembly ergonomics is set- ting up the assembly plant, and currently our digital models are limited to static evaluation. Tey give us a snapshot in time. If the question is, ‘Can I reach something?,’ Jack and Jill can move and answer ‘Yep, I can,’ or ‘No, I can’t.’ But, if I want someone to lift a large piece of carpet, manipulate it, and move it into a car, I’ll call on Santos. Te exciting thing about Santos is that he will have data on movement.” Stephens hopes that by the end of the year, Santos, now in beta, will be doing the dynamic evaluations she has in mind at Ford. In addi- tion to giving the VSR team information on what data they needed, Stephens has helped the team understand exactly what they want Santos to do. “We were able to say, ‘Tis is what we want to see, this is where we want instant feedback, and this is how we want to manipulate some- thing,” Stephens says. “Santos will do lifting and push-pull evaluations because those are things I use regularly. Part of our job is to make sure we set up the factory line correctly is better for the spine—to cradle the carpet or put one hand above and below? Should San- tos roll the carpet into a smaller size? We can evaluate all those impacts of moving the carpet into the vehicle.” Similarly, Stephens plans to have Santos help Santos determines how much load this digital soldier can bear and still assume this position. Digital bones and joints move his skin. He does not have soft tissue at his joints, nor does the software simulate fat and tissue for his whole body yet, though finite-element analysis helps researchers evaluate potential injury from blasts to limbs and internal organs. and minimize the risk of injury. We also know if we can guarantee that someone can do a task car after car without inducing fatigue; it has a huge impact on quality.” For example, the ergonomics specialists at Ford use Jack and Jill now to calculate fatigue factors—to know, for example, how many hoses someone could install and how many electrical connectors the person could snap together during a workday. “I have some data about that,” Stephens says, “but I don’t have the data across the board in every posture and every action. I’m using a broad brush. Santos will give me specific data for fatigue on the muscles in that simulation.” Stephens also expects Santos to help them understand how a worker can most efficiently and safely install a carpet, a heater, or a seat into a vehicle. “I have the carpet in CAD, and all the parts of the car,” Stephens says. “So we can decide where to put Santos’s hands. Which Predictive Dynamics A technical paper—“Structural and Multidisciplinary Optimi- zation” (April 2010) by Timothy Marler, Karim Abdel-Malek, Jasbir Arora, and others, and published in the Springer-Verlag journal—describes an approach they took in developing San- tos’s predictive dynamics. In the paper, they first state the two classifications for the dynamic analysis of mechanical system: forward dynamics, which starts with a known force and solves for an unknown response by integrating differential motion equations; and inverse dynamics, which starts with the response and solves for the unknown force by directly evaluat- ing motion equations. The problem, they posit, is that for many biosystems, force and response are unknown. Moreover, joint angle profiles, torque profiles, and ground reaction forces are unknown, as well. “In 34 July 2010 such cases,” they write, “the concept of predictive dynamics can be used to solve the problem. The basic idea is to use optimiza- tion methods to reveal force and response histories based on the available information about the dynamic system.” Predictive dynamics, they explain, avoids direct integration of differential algebraic equations to create simulations. “Instead,” they write, “it formulates an optimization problem by defining appropriate performance measure and constraints to recover the real motion of the dynamic system. In the formulation, both kinematics and kinetics parameters serve as unknowns, and equations of motion are treated as equality constraints. And, procedures to choose physical performance measure and ap- propriate constraints based on the available information are presented.” –Barbara Robertson her minimize the stress workers face when un- loading tires from a transport truck. “We don’t know how to evaluate that now,” she says. “Te tires come 700 to 750 in the back of the truck, laced in there. It’s incredibly hot in the summer, and the tires sweat and get condensation on them. We have portable air conditioners, but it’s a nasty job. I can tell Santos it’s 90 degrees in the truck. Santos will calculate the energy it takes to lift the tires out of the truck and, given the tem- perature, recommend how long the person can work. We’ll be able to do a work/rest schedule for this high-demanding job.” Santos’s first day on the job at Ford also sig- nals the first of what SantosHuman hopes will be many jobs in many other industries. “We have multiple licensing scenarios,” Johnson says. “Right now, we have maybe 100 people in some large corporations actively engaged in creating simulations and testing and deploy- ing the software internally. Currently, our tool is using sophisticated science to solve difficult problems by expert users. But, if you tweak that science, millions of people could use San- tos. Tat’s the next part.” Someday, we might spot Santos testing run- ning shoes, evaluating swimming suits for an Olympic team, assisting physical therapists with rehabilitation plans, helping stunt doubles prepare for shots in a feature film, and perhaps even, taking a starring role in a feature film. n Barbara Robertson is an award-winning writer and a contributing editor for Computer Graphics World. She can be reached at BarbaraRR@comcast.net.

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